Topics - Deactivation
The term deactivation, when pertaining to chromatography, is a chemical process that is used to treat chromatographic surfaces that come in contact with the eluting solutes. Many glass and metal surfaces together with chromatography supports are chemically active which can cause solute adsorption and subsequent peak tailing. There are two common sources of chemical activity on surfaces and they are hydroxyl groups and heavy metal ions. Heavy-metal ions can occur on glass surfaces and on the surface of gas chromatography supports (diatomaceous earths which are basically the skeletons of diatoms). The heavy-metal ions are removed by treatment with hydrochloric acid (sometimes containing a detergent) and subsequent washing with water. This procedure also tends to result in an increase in hydroxyl groups on the glass or silicate surfaces which will also cause peak tailing. The hydroxyl groups are finally ‘blocked’ by treatment with an appropriate solution of hexamethyldisilazane. Fused silica capillary columns are also deactivated in the same way by treatment with hydrochloric acid, washing with water and acetone and then treatment with a solution of hexamethyldisilazane. The deactivation of metal connecting tubes and other metal components of the chromatographic system usually consists of washing with methylene dichloride, then with acetone, then with dilute acid containing detergent, then with water and finally with acetone or ethanol to remove the last traces of water. After synthesis, bonded phases often contain residues of unreacted hydroxyl groups which can also be deactivated with hexamethyldisilazane.